The present invention relates generally to a magnetic head that has controlled thermal expansion. In particular, the present invention relates to a magnetic head having an actuator and a void region.
Magnetic data storage and retrieval systems store and retrieve information on magnetic media. In a magnetic data storage and retrieval system, a magnetic head typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving the magnetically-encoded information from the magnetic media. To write data to the magnetic media, an electrical current is caused to flow through a conductive write coil to induce a magnetic field in a write pole. By reversing the direction of the current through the write coil, the polarity of the data written to the magnetic media is also reversed.
The magnetic head is supported relative to a magnetic media surface by a slider. During operation, the disc is rotated by a spindle motor which creates airflow along a storage interface surface (SIS) of the slider from a leading edge to a trailing edge of the slider. Airflow along the SIS of the slider creates a hydrodynamic lifting force so the head of the slider essentially flies above the surface of the magnetic media. The distance between the slider and the magnetic media is known as the fly height.
During operation of the magnetic data storage and retrieval system, the fly height is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the magnetic head. Performance of the magnetic head depends primarily upon head-media spacing (HMS). High density recording preferably requires a small HMS and a low fly height. Prior to using each magnetic head, there are small variations in fly height that must be accounted for due to changing operating conditions and head-to-head variations.
Current magnetic head designs use an actuator to heat the transducer and reduce the HMS by controlled thermal expansion of the transducer. The actuator is typically placed close to, or even inside, the writer coil to maximize heating of the writer. For effective operation, the actuator must provide a large enough stroke when the write pole is either close to the magnetic media or only slightly recessed from the point at the storage interface surface where the writer protrudes most. In addition, the fly clearance must be measured for each magnetic head by a controlled measurable non-destructive head-media contact so that the proper algorithm for operating the actuator is used for each magnetic head.
In order to compensate for variations of fly height due to both head-to-head variations and changing operating conditions, the actuator provides adjustments. For applications where power supplies are limited or low power dissipation is required, actuator designs must be efficient enough to provide the needed HMS within the power requirements. These designs must actuate both the reader and the writer in order to achieve optimal efficiency. However, current designs have limited stroke and excessive power requirements due to the actuator being mechanically constrained and thermally heat sunk to the slider by the alumina basecoat.
Further, the differing mechanical and chemical properties of the substrate and transducer layers further affect the SIS during operation of the magnetic head. As the magnetic data storage and retrieval system is operated, the magnetic head is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the magnetic head itself, or a part hereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the magnetic head.
The coefficient of thermal expansion (CTE) is a measure of the change in length of a unit length of material for an incremental change in temperature. The CTE of materials used in forming the substrate is typically much smaller that the CTE of materials used in forming the metallic layers of the transducer. Due to the larger CTE of the metallic layer, those layers tend to expand a greater amount than the substrate. Thus, when the transducer is subjected to higher operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate, affecting the pole tip recession (PTR) of the transducer. This change in PTR caused by temperature is referred to as the Thermal PTR (TPTR). The PTR of a particular layer is defined as the distance between the planar SIS of the substrate and the planar SIS of that layer.
To keep the distance between the transducer and the magnetic media constant, PTR should not change significantly with temperature. If TPTR is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring the low-temperature fly height to be high enough to accommodate this variation at higher operating temperatures. Much of the TPTR originates from the metallic layers exposed at the SIS. It is the mismatch in the CTEs between the metallic layers of the transducer and the substrate material (which forms the SIS) that gives rise to the thermal protrusion. Thus, there is a need in the art for a magnetic head design that decouples the metallic layers of the transducer from the substrate.